The invention relates to a weighing scale, in particular a weighing module with a housing that encloses a weighing cell on all sides, with a force transfer member designed to be connected to a load-receiving device, wherein the force transfer member passes through an opening in a wall of the housing and is rigidly connected to a vertically movable part of the weighing cell.
Weighing scales or weighing modules of this kind are used primarily in an industrial environment, for example in the form of so-called belt conveyor scales in which the weighing module is arranged for example under a belt conveyor, to weigh objects that are transported on the conveyor belt. However, the environment in which a weighing module of this kind is installed is often very dusty. This means that the weighing module needs to be enclosed by a protective housing and that it needs to be protected against the penetration of dust in particular in the areas where the housing has openings to the outside. Particularly critical in this regard is the opening that serves as passage for the force transfer member through the housing wall. Obviously, this opening is unavoidable in order to allow a load-receiving device to be connected to the vertically movable part of the weighing cell. The state of the art offers a variety of measures that are proposed as a means of avoiding the penetration of dirt into the interior of a weighing module housing, also referred to interchangeably as a “scale housing.”
For example, commonly-owned U.S. Pat. No. 6,600,112 discloses a weighing scale with an arresting mechanism that performs a sealing function. The arresting mechanism consists of an elastic device that can be made to expand and contract so that it provides a tight-fitting contact between a stationary part that is connected to the scale housing and a part which, under a load, is movable relative to the scale housing. This device releases the movable part of the scale during the weighing process while holding it immobilized during the rest of the time. The arresting mechanism has at the same time a certain sealing effect which is particularly effective if the elastic device is arranged between the force transfer member and the scale housing. This arrangement prevents the penetration of dust into the interior of the scale housing to a large extent. A further measure which is disclosed in the same reference consists of providing the force transfer member with a cup-shaped cap which may be part of a labyrinth baffle.
These measures may provide adequate protection against the penetration of dust even in an exceptionally dusty environment, but they create the problem that there is only a relatively small gap between the stationary housing of the weighing module and the vertically movable force transfer member with the attached cap, which entails the risk that a dust bridge will form, as a mechanical connection so-to-speak, between the two parts. The dust can be airborne dust or material to be weighed that has fallen down from the load-receiving device. In weighing modules that are equipped with a sensitive, high-resolution weighing cell, this kind of a dust bridge can be enough to establish a mechanical short circuit and thereby introduce errors in the weighing result.
Therefore, the task set for the invention is to improve a scale, and in particular a weighing module, in the sense that the formation of a “dust bridge” between the stationary housing and the movable part of the scale is avoided.